(1) To isolate, in tissue culture, cell lines from human endometrium which are measurably responsive to estradiol and progesterone and contain high-affinity specific binding proteins (receptors) for those steroids. (2) To isolate, if possible, cells of the glandular epithelium, since this is the component of the tissue which gives rise to cancer. (3) To characterize and quantify the binding proteins (receptors) for estradiol and progesterone. (4) To find in vitro conditions which reliably increase or decrease the levels of these receptors. (5) To find a conveniently measured parameter such as induction of an enzyme or secretion or specific protein, which is increased by the addition of progesterone to the culture medium. (6) To compare the behavior or cell lines derived from endometrial carcinoma with the normal cell lines in respect to the factors listed above. (7) To devise an assay system applicable to cancerous endometrial tissue which can measure its ability to respond to progesterone.